81561281 has 8 divisors (see below), whose sum is σ = 85937280. Its totient is φ = 77193648.

The previous prime is 81561269. The next prime is 81561307. The reversal of 81561281 is 18216518.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81561281 - 2¹⁰ = 81560257 is a prime.

It is a super-2 number, since 2×81561281² = 13304485116721922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81521281) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 34520 + ... + 36806.

It is an arithmetic number, because the mean of its divisors is an integer number (10742160).

Almost surely, 2^81561281 is an apocalyptic number.

It is an amenable number.

81561281 is a deficient number, since it is larger than the sum of its proper divisors (4375999).

81561281 is a wasteful number, since it uses less digits than its factorization.

81561281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4183.

The product of its digits is 3840, while the sum is 32.

The square root of 81561281 is about 9031.1284455488. The cubic root of 81561281 is about 433.6719632496.

Adding to 81561281 its reverse (18216518), we get a palindrome (99777799).

The spelling of 81561281 in words is "eighty-one million, five hundred sixty-one thousand, two hundred eighty-one".